The present invention relates generally to the processing of fluid media by filtration. In particular, the present invention relates to the processing of a wide range of fluid media in order to separate and/or collect substances carried by such media.
The fluids used in nuclear power plants and at other manufacturing and processing facilities can be contaminated with substances that should not be directly released into the environment, or, on the other hand, may carry valuable or useful substances such as metals, ceramics, pharmaceuticals, or biotechnical materials or compounds. In either case, the fluid media from such facilities must be processed to remove unwanted or undesired constituents of the fluid prior to discharge or reuse, and/or processed to collect the desired valuable or useful substances. The fluid media can come from a variety of sources including, but not limited to, industrial, power generation utilities and other similar sources of fluids and exhaust gases; spent fuel pools; floor drains from nuclear power and industrial facilities; resin tank drains; evaporator bottoms; and the source of fluids can come from other fluid processes including, but not limited to, those used in metal finishing and/or recovery operations; pharmaceutical synthesization or fabrication; ceramic production; hydrometallurgical and mining applications; coal cleaning; hydrothermal processing; mineral beneficiation; and biotechnical material or compound collection. Because of environmental concerns, increasing disposal costs and other economic considerations, the separation of the contaminants and/or the valuable or useful substances from the fluids that carry them has become more and more important. The goals of this separation can include: (1) the removal and concentration of a sufficient amount of contamination from the fluid so that the resulting effluent can be reused or released to the environment after further processing, or, in some cases, directly released or reused; (2) the removal and concentration of a significant percentage of the valuable or useful substances carried by the fluid; (3) the reduction of the volume of waste that must be disposed of, and/or (4) the availability of a highly concentrated form of valuable materials suitable for economical recovery or recycling.
A number of techniques are used to attempt to separate substances from fluids, including filtration, ion exchange, evaporation, crystallization and adsorption. Generally, filtration is a process in which a separating medium or device (i.e., a filter) capable of removing small particles from a gas or liquid by mechanical (or diffusion based) interception is used to separate such small particles (i.e., the “reject” and/or “concentrate”) from the fluid that passes through the separating medium or device (i.e., the “filtrate” and/or “permeate”). Also, the separation of the substances from the fluid by filtration is generally based on the difference between the size of the particles of the substance and the openings in the filter medium, but sometimes filtration is also aided by electrostatic forces, hydrophobic/hydrophilic interactions and other interfacial phenomena that enhance or preclude selective species transport across the membrane, and/or by chemical reactions. Moreover, with respect to filtration and ion exchange, the collected substances can be particulate and/or dissolved ions of varying sizes, which commonly requires these two techniques to be used in a particular sequence.
Sometimes more than one type of filter is used. For example, in a standard single-pass filtration process, roughing filters are first used to remove larger particles, and then ever finer, polishing filters (i.e., those filters that are potentially capable of removing smaller and smaller sized particulate including, but not limited to, screen filters, microfilters, ultra filters, nano-filters, and hyper filters, i.e., reverse osmosis membranes) are used to remove smaller particles. By using the various types and sizes of filters in this manner, this filtration process may be able to remove a high percentage of the particulate while attempting to protect the finer membranes from the damage that could be caused by larger particles. Therefore, it is standard practice to use various sized (and/or types of) filters in a specific sequence; with the coarser filters (i.e., filters having larger particle collection size ratings) being used first in an attempt to remove the larger particulate, then ever finer filters in an attempt to remove the smaller particulate.
The philosophy of this approach makes good sense for several reasons, especially when considered from the perspective of having a fluid medium that is carrying a moderate level of particulate. In such an environment, if a fine filter is used first, the amount of particulate it would remove would be so great that the filter would quickly become fouled with both fine and coarse particulate, which would cause the flow through the filter to stop altogether, and which could occur soon after being placed in service. Therefore, by using filters in sequence, from coarse (roughing) to fine (polishing), attempts to assure that the throughput of each filter is as high as possible. Furthermore, because filters with smaller pore size are generally more expensive, it makes better economic sense to use the finer filters for filtering only the smallest particles and not also for filtering out particles that could be removed from the fluid with less expensive filters. Additionally, some fluid media require further substance removal after filtration in order to attempt to remove dissolved substances from the fluid. This is generally accomplished by sending the filtrate from the last filter, or set of filters, to an ion exchanger and/or a reverse osmosis unit, which, in combination with the standard filtering method, may result in producing a treated fluid that can be nearly free of both particulate and dissolved species.
The processes just described can work well, and, in general, produce clean filtrates and/or permeates, potentially remove many of the substances carried by the fluid, and may allow for the safe disposal of the unwanted substances. However, they focus solely on obtaining a clean filtrate and not on obtaining an efficient volume of collected materials, which would be economically beneficial, if obtained, i.e., an efficient volume of collected materials would essentially consist of only those substances intended to be collected.
Furthermore, because of environmental concerns and the rising costs associated with the disposal of unwanted substances, e.g., radioactive, toxic, and/or hazardous waste, there is a growing need to make a concerted effort to reduce the volume of the wastes being disposed of, and, because it is also desirable to recover valuable and/or useful substances carried by some fluid media—especially in a highly concentrated form—there is also a need for a way to process such fluid media so that the valuable and/or useful substances can be efficiently and relatively inexpensively collected and/or recovered. Therefore, based on the foregoing, a need remains to remove substances from various fluid media in a way that results in an efficient collection of such substances, provides for easier handling of the substances collected, and does not compromise the quality of the filtrate and/or permeate produced.